Another myth is that marijuana's potency today is much higher than it was in say the 60s and 70s when marijuana began to bubble up into the mainstream culture. Are these true?

The hard data on potency from the 1960s are scanty, but it is clear that potency of seized marijuana has increased over the time period for which there are abundant data (from about 1980 forward). The increase takes two forms: increased potency within a particular “type” of marijuana (e.g., commercial grade marijuana today is more potent than it was in the past) and shifts in market share (e.g., the market share of sinsemilla has been growing at the expense of commercial grade). The extent of the increase has been exaggerated in some sources, but the actual increases are substantial: at least a factor of two, maybe more.

The other notable change between the 1960s and subsequent periods is the age of users, and their socio-economic class. In the 1960s, marijuana use was associated with college students. By the 1980s, the median age of initiation had fallen substantially, so initiation is more of a middle-school and high-school phenomenon. College graduates are also now a modest subset of the market, accounting for perhaps one-seventh of consumption. The majority of demand among adult users comes from those with a high-school education or less.